Catalytic converters are universally employed for oxidation of carbon monoxide and hydrocarbons and reduction of the oxides of nitrogen in automobile exhaust gas streams. A catalyst substrate comprising a catalyst, disposed within the shell of the catalytic converter, facilitates the oxidation and reduction process of the exhaust gas stream. Catalyst substrates tend to be frangible and have coefficients of thermal expansion differing markedly from their metal, usually stainless steel, shells. As a result, the mounting means of the substrate, typically a mat support material disposed between the catalyst substrate and the shell, must provide resistance to mechanical shock due to impacts and vibrations and to thermal shock due to thermal cycling. Both thermal and mechanical shock may cause deterioration of the mat support material, which once started, quickly accelerates and ultimately renders the device useless.
Intumescent and non-intumescent sheet mat support materials do an adequate job of holding the substrate in place while resisting erosion at moderate exhaust temperatures, and moderate pressure pulsations of the exhaust gas. However, when positioning the catalytic converter closer to the engine exhaust manifold, the converter, including the mat support materials are subjected to much higher exhaust temperatures. Under these conditions, over a period of time, existing mat support materials can be eroded.
A catalytic converter may be placed anywhere in the exhaust system. However, it is advantageous to locate a catalytic converter as close as possible to the combustion chamber in an engine compartment. Placing a catalytic converter closer to the combustion chamber quickens the converter's light-off time. The light-off time is the point at which the catalyst reaches fifty percent efficiency over a period of time (measured in seconds) during start-up of the automobile.
Placing catalytic converters into an engine compartment, however, creates additional packaging constraints. “Packaging constraints” is an industrial term referring to the question, “how do we fit a part in a vehicle?”, taking into consideration the space and volume of the area of interest, including the parts nearby and the interaction of those parts.
Generally, a catalytic converter 20 utilizes a pair of endcone assemblies 22 welded onto a shell 30 to provide a gas tight seal and for attaching the converter to the mobile vehicle's exhaust system (See FIGS. 1 and 2). Typically, endcone assemblies 22 comprise both an outer endcone 24 and an inner endcone 26. Inner endcone 26 reduces the likelihood of mat erosion and thermal deterioration of a mat support material 28 during operation of converter 20. Inner endcone 26 is welded into outer endcone 24 using a costly and inefficient manufacturing procedure. When outer endcone 24 is welded onto shell 30, inner endcone 26 is inserted “blind” into mat support material 28, which is wrapped around a catalyst substrate 32 and concentrically disposed within shell 30 (FIG. 2). The “blind” insertion of inner endcone 26 can periodically cause catalyst substrate 32 to break during assembly of converter 20. As a result, alternatives are being sought for inner endcone 26.
Some catalytic converter designs, and especially designs without inner endcones, incorporate an edge protection material around the intake area of the catalyst substrate to reduce thermal deterioration of the mat support material (e.g., mat protection ring or endring). Incorporating edge protection materials while assembling a catalytic converter, however, requires additional labor. In addition, edge protection materials increase the overall weight of the catalytic converter as well as its cost. This, in turn, ultimately reduces the chances of meeting the customer's requirements.
A catalyst disposed on a frangible substrate is supported within the catalytic converter to facilitate the oxidation and reduction process of the exhaust gas stream. During operation, the exhaust gases pass over the substrate and contact the catalyst where the amount of hydrocarbons, carbon monoxide, and oxides of nitrogen are reduced. The temperature of the catalyst is typically between 750° C. and 950° C. and may be higher depending upon the location of the catalytic converter relative to the engine of the automobile. To lessen the effects of this high temperature, a support material cushions and insulates the catalyst material from a housing in which the substrate and catalyst are mounted.
Currently, manifold converters are manufactured by welding cast or fabricated exhaust manifolds to a catalytic converter shell. Thin-wall castings are also available that incorporate the converter shell and manifold into a single casting. Fabricated manifolds are easily joined to converter shells, but are difficult to manufacture compared to a casting of the same. Conventional welding techniques have been commonly used to form and join these catalytic converters to exhaust manifolds. However, the microstructure of nodular cast iron exhaust manifolds is not designed for welding. If welded, the microstructure has a band of high hardness martensite immediately adjacent to the weld in the heat-affected zone. A welding filler metal with intermediate thermomechanical properties having a sufficient high temperature strength and toughness is required for the manifold converter to survive. The welding filler is quite expensive, however, and the welding operation must be closely monitored.
Thin-walled castings eliminate the welding operation, but the thin-walled castings are still 3–4 mm thick compared to the 1.5 mm thick wrought shell. The thin-walled castings add mass and decrease converter performance due to the increased thickness. On the other hand, cast and fabricated stainless steel manifolds eliminate the cast iron welding difficulties, but are extremely expensive.
In addition, the drawbacks of conventional welding techniques include the creation of a high amount of heat that risks damage to the parts being welded. Another drawback is that dissimilar metals and work pieces of different gauge thicknesses cannot be joined, thereby limiting the materials used in forming catalytic converters. Lastly, conventional designs of the sheet metal or cast-metal heat resistant shells incorporate several welding steps. Welding is not only costly from an equipment standpoint due to the amount of materials, consumables, and labor associated with the process, but also leads to considerable in-plant control costs and warranty.
Accordingly, there remains a need in the art for an apparatus and method for manufacturing a catalytic converter attachable to an exhaust manifold without a welded joint that is cost effective.